After a nine-month delay for repairs in Hawaii, the Solar Impulse round-the-world flight attempt resumed with a two-day, 14h flight to NASA’s Moffett Field, near San Francisco.

This ninth leg of a bid to circle the world on solar power alone followed a five-day/five-night flight from Japan last July, which set solar-powered endurance records but destroyed the single-pilot aircraft’s batteries.

Solar Impulse 2 manages a 24h flight cycle by ascending to 28,000ft during daylight and gradually descending overnight as its batteries run down. During the Japan-Hawaii flight, the batteries overheated while charging.

The aircraft has a wingspan of 72m (236ft) – a Boeing 747-8I measures 68.5m – but weighs a mere 2,300kg (5,071lb) including the lithium batteries and solar cells. It flies at speeds of 27-54kt (50-100 km/h).

The Switzerland-based project – described by creators and co-pilots André Borschberg and Bertrand Piccard, who flew the leg to Moffett, as a demonstration of energy efficiency technology rather than a pure aviation challenge – will resume with a multi-leg hop to New York before crossing the Atlantic to return to Abu Dhabi, where the flight began in March 2015.